The present invention relates to a bias distribution network, and more particularly to a bias distribution network for a memory.
Mixed mode non-volatile memory integrated circuit systems typically use bias across wide dimensions on a chip. Bias levels typically varies across the chip, because of physical boundary, power supply and temperature variation, or across multiple lots. However, a level bias across the chip is desired to ensure consistent performance for each memory cell, such as during programming or reading. For multilevel flash memory, the desire for a level bias is even more severe due to smaller margin per voltage level.
The present invention provides a memory device that has bias levels that are more consistent across the device.
The present invention also provides a testing method and apparatus to monitor and force the bias level.
The present invention provides a memory device that comprises an array of memory cells arranged in rows and columns. A portion of the array of memory cells is divided into segments. A global bias circuit generates a plurality of first bias currents. A plurality of local bias networks each comprise a local bias circuit that generates a plurality of second bias currents in response to a corresponding one of the plurality of first bias currents, and each comprises a plurality of segment bias circuits generating a third bias current. Each segment bias circuit is adjacent to a corresponding segment of said memory cells.
In one aspect, each segment bias circuit may provide a ground feedback signal to the local bias circuit, and in response thereto the local bias circuit adjusts the second bias current.
In one aspect, the segment bias circuits may be disposed in geometric positions in the segments.
In one aspect, the global bias circuit may include a global trim circuit to adjust the plurality of first bias currents in response to a global trim signal. Each local bias network may include a local trim circuit to adjust the plurality of second bias currents in response to a local trim signal.